The former sprinter, who previously held the 200 and 400 metres world record, revealed on Twitter on Saturday that he had suffered a transient ischemic attack.
However, Johnson added that he is making "great progress" and took the opportunity to raise stroke awareness.
"Last week, I rather surprisingly suffered what's known as a Transient Ischemic Attack or mini stroke," the American posted on his social media page.
Known for his trademark stiff, upright running style, Johnson is one of athletics' most famous figures after dominating the 200m and 400m for close to a decade in the 1990s.
His 19.32-second winning time at those Games was the largest ever improvement on a 200m world record and remained the fastest time in history for a dozen years until Usain Bolt surpassed it at the 2008 Olympics.
"The good news is I'm back at home with my family, cleared of any heart issues and have already made great progress on my road to a full recovery.
"It seems these things can affect anyone, even the once fastest man in the world! I'm no stranger to a good exercise plan and have thrown myself into it with my usual focus and determination.
"In these situations being a former athlete has really helped with mindset but also a reminder that you need to take care of yourself.
"I will be posting updates on my recovery often. Thanks for all the words of encouragement."
Johnson's initial post received messages of support from fellow athletics stars Jessica Ennis-Hill, Colin Jackson and Denise Lewis.